Rörelsemoment

Rörelsemoment, often referred to as angular momentum in English, is a fundamental concept in physics that describes the rotational inertia of an object. It is the rotational analogue of linear momentum and is a conserved quantity in a closed system, meaning its total value remains constant unless acted upon by an external torque.

The magnitude of an object's rörelsemoment depends on three factors: its mass, how that mass is distributed relative to the axis of rotation, and how fast it is rotating. Mathematically, it is often expressed as the product of the moment of inertia (which quantifies the resistance to rotational acceleration) and the angular velocity (the rate of rotational change).

This principle of conservation of rörelsemoment has numerous observable consequences. For example, a figure skater spinning will increase their rotational speed as they pull their arms in, thereby decreasing their moment of inertia. Conversely, extending their arms increases their moment of inertia and slows down their spin. Similarly, a spinning top or a gyroscope maintains its orientation due to the conservation of its rörelsemoment, resisting changes in its axis of rotation. In astrophysics, the formation of galaxies and planetary systems is also governed by this principle, as the initial slight rotation of interstellar gas clouds is amplified as they collapse under gravity.